Uniform, metal oxide nanoparticles having a diameter of about 1-100 nanometers (nm) are used in magnetic recording media, ceramics (e.g. cobalt oxide), semiconductors, gas sensors (e.g. tin oxide), catalyst supports (e.g. alumina), reinforcing agents (e.g. silica), and other important applications. The following papers and patents describe a variety of combustion-based and plasma-based methods and apparatus for generating metal oxide nanoparticles.
“Plasma Production of Metallic Nanoparticles” to C. Chou and J. Phillips, in J. Mater. Res., vol. 7, no. 8, August 1992, pp. 2107-2113, describes the production of iron or iron oxide nanoparticles from ferrocene using a microwave plasma torch apparatus. Oxygen, hydrogen, and argon were used to create the plasma and to transport the ferrocene to the coupler region (i.e. to the plasma) or to the afterglow region upstream of the plasma. In either case, when an microwave-generated oxygen plasma was used, iron oxide nanoparticles were produced.
“Synthesis of Nanosized Ceramic Oxide Powders by Microwave Plasma Reactions” to D. Vollath and K. E. Sickafus, in Nanostructured Materials, vol. 1, pp. 427-437, 1992, describes the production of alumina (i.e. aluminum oxide, Al2O3) titania (i.e. titanium oxide, TiO2), and zirconia (i.e. zirconium oxide, ZrO2) from the corresponding metal chloride compounds using a microwave-generated plasma.
U.S. Pat. No. 5,514,350 to B. H. Kear et al. entitled “Apparatus for Making Nanostructured Ceramic Powders and Whiskers,” which issued May 7, 1996, describes an apparatus used to prepare non-agglomerated nanostructured ceramic powders from metal organic precursors.
“Synthesis of Oxide Nanoparticles” to G. Skandan et al. in Nanostructured Materials, vol. 11, no. 2, pp. 149-158, 1999, describes the production of nanoparticles of silica, titania, and alumina from hexamethyldisilazane, titanium ethoxide, and aluminum tri-sec butoxide respectively, by a combustion flame-chemical vapor condensation process.
U.S. Pat. No. 5,876,683 to N. Glumac et al. entitled “Combustion Flame Synthesis of Nanophase Materials,” which issued May 2, 1999, describes a low-pressure combustion flame process for preparing nanophase powders from metal organic precursors using a flat flame combustor.
U.S. Pat. No. 6,254,940 to S. E. Pratsinis et al. entitled “Electrically Assisted Synthesis of Particles and Film With Precisely Controlled Characteristic,” which issued Jul. 3, 2001, describes the production of nanoparticles. Boric acid, BCl3 borane, SiCl4, chlorosilane, silane, metal halide, partially hydrated metal halide, metal hydride, metal alcoholate, metal alkyl, metal amide, metal azide, metal boronate, metal carbonyl, and combinations of these materials are heated in a flame reactor and passed between plate electrodes to form the nanoparticles.
Preferred methods are cost effective, employ relatively inexpensive precursor materials, generate minimal waste, and are continuous i.e. are not halted to replenish the supply of precursor as it is converted to product. Cost-effective, continuous methods for producing uniform, high purity, metal oxide nanoparticles remain desirable.
Therefore, an object of the present invention is to provide a continuous method for producing metal oxide nanoparticles.
Another object of the present invention is to provide a method for producing metal oxide nanoparticles from inexpensive precursor materials.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.